Networking 101

[red_ned]

Networking 101
The basics for using networks, i wont bother with transport layers etc unless people really want it.

Some basic terms you need:

1. MAC Address - Media Access Control
Each network card has a unique 48bit address which identifies the computer on the network. In fact it is through mac addresses that
computers actually communicate to each other, we have just added more simplistic layers on top like Ip then DNS.
MAC addresses are expressed in 12 Hexadecimal numbers like 48-3F-0A-91-00-BC, some numbers are reserved for the manufacturers so you can tell who makes them.

2. IP - Internet protocol
Standard 32bit IP(IP v4) is X.X.X.X in theory from 0.0.0.0 to 255.255.255.255.
32 bit is due to 255 being made of 8 binary bits so 8+8+8+8.
New standard 128bit IP(IP v6) is the new Ip range which looks like:
0000:0000:0000:0000:0000:0000:C0A8:6420 (which is actually 192.168.100.32).
128 bit is due to 8+8+8.... etc but is expressed not in binary but in hexadecimal but (like the example above) can be backwards compatible with 32 bit addresses.

3. DHCP - Dynamic Host Configuration Protocol
This is a system where the network card can negotiate a connection by asking permission and an IP from a server on a network. You dont have to set anything up unlike a Static IP setting.

4. Gateway Address
The IP of the device which connects you to other wider networks like the Internet. This can be through computers, switches or routers which directs traffic out of the local loop of the network you are on.

5. Host Mask
One of the most complex and misunderstood parts of networking which basically creates a specific sized network.
The first digits say what the network uses to identify itself, the second part says how many computers can be on that network at one time (-2 from what you would expect as i will explain later).
A big network could look like 255.0.0.0 - only 255 used for the network. Next could be 255.255.0.0, then 255.255.255.0.

If you have 2 computers on different hostmasks and IP ranges they probably wont be able to communicate and are considered to be V-LANs (virtual local area networks) or subnet.
The masks quoted are (basically though not 100% limited) to support the reserved or private range of IP's for use on Internal networks only.
255.0.0.0 caters to the 10.0.0.0 – 10.255.255.255 (24 bit or /24) IP range. Class A network - providing 16,777,216 IP's.
255.255.0.0 caters to the 172.16.0.0 – 172.31.255.255 (20 bit or /20) IP range. Class B network - providing 1,048,576 IP's.
255.255.255.0 caters to the 192.168.0.0 – 192.168.255.255 (16 bit or /16) IP range. Class C network - providing 65,536 IP's.

Get your hostmask wrong and yer buggered.


6. DNS - Domain Name Service
Ties an IP address to a name (like google.com). Huge tables sit on servers across the world which provide this information on request and also pass on routes to get there. Thats why it takes a couple of days for a new name to go round the whole internet and be visible to all.